The invention relates to a method for reducing torque ripple in AC brush-less motors with concentrated windings. AC synchronous travelling or rotating field motors with concentrated primary side windings i.e. windings in which individual coils, wound onto single primary side toothed-modules are connected together to form one phase of the motor winding, have significant performance benefits when compared to standard rotating AC field motors with overlapping or so called distributed or sine-weighted windings.
These benefits have been well understood for several years and include reduced power loss, increased torque density, simplified and more highly automated manufacturing processes and lower tooling costs. All of these advantages spring from the fact that the concentrated winding occupies less physical space than a distributed winding.
A distributed winding must traverse the motor primary side, and must be wound such that the coils of one winding overlap with those of a second winding. The difficulties in physically fitting such windings into the available space on the primary side result in reduced slot fill factor i.e. less wire in each of the primary side slots, and large lengths of wire running between the primary side slots at the ends of the motor. These so called end-windings do not contribute to torque production, but do increase the winding resistance and thus the heat losses which are proportional to the resistance, and thus reduce motor efficiency.
Concentrated winding motors on the other hand, are usually formed by winding coils onto individually produced primary side toothed-modules, which are themselves built up from multiple laminations. The wound modules are subsequently welded or otherwise joined together to form the primary side of the motor.